1. Field of the Invention
The present invention relates to a method for making a fabric comprising fibers woven in a high density and to a fabric obtained therefrom. A fabric with fibers woven in a high density is called a high density fabric. A high density fabric is used, for example, as a base cloth for an uncoated air bags installed in motor vehicles. The high density fabric used as the base cloth of uncoated air bags is required to have a low air permeability.
The present invention provides an efficient production method of a fabric having a high density and a low air permeability, by improving the conventional weaving method of fabric.
2. Description of the Prior Arts
It is desired to develop air bags which can assure higher safety of passengers of motor vehicles. A sensor detects an impact of a car collision and immediately after the detection, a high temperature high pressure gas is produced in an air bag, and the air bag is instantaneously inflated by the gas. Therefore, the woven fabric forming the air bag is required to have a high density and a uniform low air permeability.
Air bags are classified into coated air bags formed with a base cloth coated on its surface with an urethane or silicone resin, etc., and uncoated air bags formed with a base cloth having no coating on its surface.
Uncoated base cloths and uncoated air bags made therefrom are disclosed in Japanese Patent Laid-Open (Kokai) Nos. Hei 4-2835 and Hei 6-146132 and U.S. Pat. Nos. 4,977,016 and 5,073,418.
The uncoated base cloths for air bags are woven by a water jet loom (hereinafter abbreviated as WJL) with the shedding motion of the healds performed by a crank mechanism or a rapier loom. However, the base cloths obtained by them cannot be said to be high density fabrics having a desired uniform low air permeability.
Where the shedding of the healds is carried out by a crank mechanism, the shedding time of the healds is short. Therefore, at the time of picking motion, weft yarns are less likely to be flown sufficiently and stably. Therefore, the water jet flow collides with the warp yarns and fluffs are generated on the warp yarns. As a result, the weaving quality is remarkably degraded.
To solve the problem, it can be considered to raise the water jet pressure. However, if the water jet pressure is raised, it causes a high tension acting on the weft yarns and excessive weave contraction which bring down difficulty in weaving. This method does not improve quality of weaving.
It can also be considered to weave at a higher warp tension. However, if the warp tension is higher, friction of warp yarns with the reed and the healds increases at the time of beating motion and shredding motion and it causes problems of warp breakage and warp fluffing. This method does not improve quality of weaving.
As another problem, a fabric having a higher density has larger weave contraction in the weft direction immediately after completion of weaving. Because of large weave contraction, the difference between the denting width and the weave width becomes large, and a phenomenon that the warp yarns beside the selvages are strongly scrubbed by the reed is observed. This phenomenon causes warp fluffing and warp breakage, and must be eliminated to obtain a desired high density fabric.